Vehicle clutches of the diaphragm spring type typically include a flywheel, a clutch disc splined onto a driven shaft, an axially movable pressure plate rotatable with the flywheel, a fulcrum surface on or operatively connected to the pressure plate, a clutch cover secured to the flywheel, a diaphragm spring engaging the fulcrum surface on the pressure plate and a separate fulcrum surface on the cover, and a release bearing axially reciprocable on the driven shaft to engage radially inwardly extending fingers of the diaphragm spring. During actuation of the diaphragm spring by the release bearing to retract or advance the pressure plate, the spring will pivot about a wire pivot ring in the clutch cover with the outer edge of the spring engaging the pressure plate fulcrum. Upon release and re-engagement of the clutch, all of the parts will retain the same relationship.
The characteristic curve of a Belleville spring as employed in most clutches provides a plate load of approximately 1400 pounds when the clutch parts are new and engaged. Upon clutch release, pulling back the pressure plate 0.080 inches reduces the plate load to about 700 pounds and results in an acceptable pedal pressure for the vehicle operator. As wear occurs, the pressure plate with the clutch engaged moves toward the flywheel, such that at 0.080 inches wear of the friction facings, the plate load is increased to 2100 pounds, and when released for a distance of 0.080 inches, the load is reduced to 1400 pounds. This results in a pedal pressure approximately twice as large as the original pressure which is very objectionable to the operator.
Also, when there is wear in the system, particularly wear to the clutch friction surfaces, the diaphragm spring moves through a greater arc of travel and the release bearing must move a greater distance to effect a complete clutch release. Due to the movement of the pressure plate towards the flywheel upon friction facing wear, the change in pressure plate position forces the spring fingers of the diaphragm spring into greater pressure engagement with the release bearing which may bind the bearing against the release fork. To alleviate this problem, the vehicle operator must have the clutch serviced to reposition the release bearing. A large percentage of clutch failures in passenger cars have been due to neglect in maintaining proper adjustment of the clutch system.
To alleviate this problem, various methods of automatic adjustment were attempted with emphasis on adjusting the release bearing carrier. The present invention overcomes the present problems of clutch wear by an adjustment of the pressure plate fulcrum position relative to the flywheel.
The present invention comprehends the provision of an automatic wear adjuster for vehicle clutches of the diaphragm spring type that maintains the original load characteristics of the diaphragm spring. This is accomplished by sensing the decrease in the distance between the flywheel and pressure plate due to clutch friction facing wear when the clutch is engaged and increasing the dimension between the clutch engaging face of the pressure plate and the spring-engaging surface of the fulcrum.
The present invention also comprehends the provision of an automatic wear adjuster for a diaphragm spring clutch wherein the spring engaging fulcrum on the pressure plate comprises a pressure ring in operative engagement with the rear surface of the pressure plate having the spring fulcrum formed thereon. A cam ring is positioned between the pressure plate and pressure ring and has camming surfaces cooperating with similar cam surfaces formed on the pressure plate. Rotation of the cam ring will cause axial movement of the pressure ring relative to the pressure plate.
The present invention further comprehends the provision of an automatic wear adjuster for vehicle clutches wherein a plurality of levers sense the change in the distance between the flywheel and pressure plate due to clutch wear. The levers are pivoted on the pressure plate with one end of each lever acting to contact the clutch engaging surface of the flywheel. The opposite end of each lever is adapted to engage a projection on the cam ring, such that rotation of the levers due to contact with the flywheel upon clutch wear will cause a corresponding rotation of the cam ring to raise the pressure ring.
Further objects are to provide a construction of maximum simplicity, efficiency, economy and ease of assembly and operation, and such further objects, advantages and capabilities as will later more fully appear and are inherently possessed thereby.